Mark G. Shilton

Bio: Mark G. Shilton is an academic researcher from University of Leeds. The author has contributed to research in topics: Tetrahydrate & Conductivity. The author has an hindex of 11, co-authored 12 publications receiving 620 citations.

Rapid H+ conductivity in hydrogen uranyl phosphate-A solid H+ electrolyte

Abstract: We have found that the layered hydrate HUO2PO4. 4H2O is a rapid proton conductor. The room temperature conductivity of 4 × 10−3ohm−1cm−1 is higher than that of Na+ in β alumina. The activation energy is 30± 3 kJ mol−1. The material is insoluble, and presses into transluscent discs suitable for solid electrolyte applications.

Studies of layered uranium(VI) compounds. I. High proton conductivity in polycrystalline hydrogen uranyl phosphate tetrahydrate

Abstract: We have found that hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O has a high proton conductivity. The ac conductivity was 0.4 ohm −1 m −1 at 290°K measured parallel to the faces of sintered disks of the compound. The activation energy was found to be 31 ± 3 kJ mole −1 . The values of conductivity were between 3 and 10 times lower when measured perpendicular to the disk faces due to preferred orientation of the plate-like crystals. Both the powder and sintered disks are stable in air and insoluble in phosphoric acid solution of pH 2.5. Experiments are described which enable possible grain boundary contributions to the conductivity to be determined in such hydrates. The extrinsic grain boundary contribution to the conductivity was found to be small from experiments in which the pH in a solution cell was varied. The abnormally high bulk H + conductivity thus inferred is attributed primarily to the high concentration of H + , which exists as H 3 O + in the interlamellar hydrogen-bonded network. A Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and intramolecular transfer steps, in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by the high concentration of H-bond vacancies.

Studies of layered uranium(VI) compounds. IV. Proton conductivity in single-crystal hydrogen uranyl phosphate tetrahydrate (HUP) and in polycrystalline hydrogen uranyl arsenate tetrahydrate (HUAs)

Abstract: Single-crystal measurements on hydrogen uranyl phosphate tetrahydrate, HUO 2 PO 4 ·4H 2 O (HUP), have confirmed that the high proton conductivity is a bulk characteristic. The conductivity values were in substantial agreement with those previously reported for polycrystalline disks. A conductivity of 0.6 ohm −1 m −1 at 290°K and an activation energy of 30 ± 1 kJ mole −1 were measured parallel to the structural layers of the crystal. The conductivity was at least 100 times lower when measured in the perpendicular direction. A reasonable attempt frequency ω 0 of approximately 10 15 Hz could be derived from the parallel conductivity on the assumption that the charge carrier concentration was equal to that of the H 3 O + ions. This implies a low proton mobility, of the order of 10 −9 m 2 V −1 sec −1 at 290°K, in support of previous estimates. We have also shown that polycrystalline hydrogen uranyl arsenate tetrahydrate, HUO 2 AsO 4 ·4H 2 O (HUAs), has a high conductivity of 0.6 ohm −1 cm −1 at 310°K, with an activation energy of 31 ± 2 kJ mole −1 . Below the respective dielectric ordering transition temperatures of HUP and HUAs of 274 and 301°K, the lower conductivity values show a marked frequency dependence, which may be due to dispersion effects caused by water reorientations.

N.M.R. study of hydrogen motion in hydrogen uranyl phosphate (HUP) and hydrogen uranyl arsenate (HUAs)

Abstract: Pulsed /sup 1/H n.m.r. measurements were made of relaxation times in hydrogen uranyl phosphate and arsenate, which are fast proton conductors. Both compounds were found to undergo a phase transition resulting in discontinuities in T/sub 1/ and T/sub 2/ and a DTA peak. This transition occurs around 274/sup 0/K in HUP and around 302/sup 0/K in HUAs. Above the transition the n.m.r. behavior of the two compounds is very similar, with an activation energy for T/sub 1/ and T/sub 2/ of 20 +- 1 kJ mol/sup -1/. The T/sub 1/ values are almost equal to T/sub 2/ values, and this can best be explained by the rapid diffusion of hydrogen. Possible mechanisms for hydrogen self-diffusion and charge transport are discussed that can account for the higher activation energies reported for the conductivities compared to those for n.m.r. relaxation.

Fabrication of films of hydrogen uranyl phosphate tetrahydrate and their use as solid electrolytes in electrochromic displays

Abstract: We have found that the high proton conductivity of hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O (HUP) is sufficient to enable an HUP/H x WO 3 electrochromic cell to function as fast as a cell with an acidic solution electrolyte. Switching times down to 0.3 s were found. The fabrication procedure to obtain the stable and uniform films of HUP required has been optimized, and dense sintered films up to 6 cm in diameter have been produced.

Proton Conductivity: Materials and Applications

Abstract: In this review the phenomenon of proton conductivity in materials and the elements of proton conduction mechanismsproton transfer, structural reorganization and diffusional motion of extended moietiesare discussed with special emphasis on proton chemistry. This is characterized by a strong proton localization within the valence electron density of electronegative species (e.g., oxygen, nitrogen) and self-localization effects due to solvent interactions which allows for significant proton diffusivities only when assisted by the dynamics of the proton environment in Grotthuss and vehicle type mechanisms. In systems with high proton density, proton/proton interactions lead to proton ordering below first-order phase transition rather than to coherent proton transfers along extended hydrogen-bond chains as is frequently suggested in textbooks of physical chemistry. There is no indication for significant proton tunneling in fast proton conduction phenomena for which almost barrierless proton transfer is suggest...

Polymers in sensor applications

Abstract: Because their chemical and physical properties may be tailored over a wide range of characteristics, the use of polymers is finding a permanent place in sophisticated electronic measuring devices such as sensors. During the last 5 years, polymers have gained tremendous recognition in the field of artificial sensor in the goal of mimicking natural sense organs. Better selectivity and rapid measurements have been achieved by replacing classical sensor materials with polymers involving nano technology and exploiting either the intrinsic or extrinsic functions of polymers. Semiconductors, semiconducting metal oxides, solid electrolytes, ionic membranes, and organic semiconductors have been the classical materials for sensor devices. The developing role of polymers as gas sensors, pH sensors, ion-selective sensors, humidity sensors, biosensor devices, etc., are reviewed and discussed in this paper. Both intrinsically conducting polymers and non-conducting polymers are used in sensor devices. Polymers used in sensor devices either participate in sensing mechanisms or immobilize the component responsible for sensing the analyte. Finally, current trends in sensor research and also challenges in future sensor research are discussed.

Rational Designs for Highly Proton-Conductive Metal-Organic Frameworks

Abstract: A novel metal−organic framework (MOF), (NH4)2(adp)[Zn2(ox)3]·3H2O (1) was synthesized and its structure was determined. We propose three types of rational design to introduce proton carriers into MOFs. The simplest method is to introduce them directly as counterions such as NH4+, H3O+, and HSO4− into the pores of frameworks (type I). The second is to put acid groups on frameworks, the protons being provided from them (type II). The third is to incorporate acidic molecules into voids (type III). 1 demonstrated a combination of two of the concepts by introducing NH4+ ions using the anionic framework (type I) and putting carboxyl end groups of adipic acid in a honeycomb-shaped void (type III). 1 showed a superprotonic conductivity of 10−2 S cm−1 at ambient temperature, comparable to organic polymers such as Nafion, which is in practical use in fuel cells. This is the first example of an MOF to exhibit a superprotonic conductivity of 10−2 S cm−1 at ambient temperature.

Electrochromic materials and devices for energy-efficient windows

Abstract: Numerous inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application. It is possible electronically to alter a window's transmission and reflection properties by use of electrochromic thin films. This allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation. As a result, an aperture can be optically and thermally managed, reducing space heating and cooling loads. The properties of transition metal oxides, such as WO 3 , MoO 3 , Ir 2 O 3 and V 2 O 5 are detailed. Organic systems such as heptyl viologen and polytungsten anion are reviewed. Also, intercalated structures are discussed. Various designs of working devices are outlined with emphasis on solid-state configurations. From this quantification, materials and devices with appropriate deposition techniques for window applications are detailed.